JPS62250640A - Detector for end point of plasma ashing - Google Patents

Abstract

PURPOSE:To detect the end point of ashing precisely and stably by detecting the intensity of light of at least two or more of spectral lines in transition light within a specific wave range from C0 in plasma and comparing the intensity of these lights. CONSTITUTION:The angle of rotation of a diffraction grating is changed and some spectral line in b<3>SIGMA-a<3>pi transition light within the range of wavelengths 296-300nm from CO is extracted, and the spectral line is projected to a photomultiplier 17, the intensity of light is converted into electric signals, and the maximum value of the electric signals is memorized temporarily in a detector 13. The diffraction grating 15 is turned, another spectral line is selected similarly, and the maximum value of the spectral line is memorized to the detector 13. The rotational temperature of plasma is obtained from the ratio of the intensity of these two maximum values, and the variation of a rotational temperature in the vicinity of an organic film and the rotational temperature of a plasma region in the vicinity of an electrode is compared from the alteration of the rotational temperature of plasma or by mounting two monochromators 14, thus detecting the end point of ashing. Accordingly, the adjustment of the detector by the change of the conditions of ashing is unnecessitated, thus stably detecting the end point of ashing accurately.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a device for detecting the end point of ashing in plasma ashing that can remove organic films such as photoresist films using oxygen plasma. be.

[Conventional technology]

FIG. 11 is a diagram showing a conventional plasma ashing end point detection device disclosed in, for example, Japanese Patent Publication No. 54-21711.
4 is a high frequency and high electric field application electrode for applying a high frequency and high electric field supplied from this power source to the reaction tube 3, and 4 is a reaction gas for introducing a reaction gas containing oxygen gas into this reaction tube 3 in the direction of arrow X. a supply pipe; 5 is a reaction gas exhaust pipe for discharging the reaction gas reacted in the reaction tube 3 in the direction of arrow Y;
6 is a wafer support set in the reaction tube 3; 7 is a large number of wafers placed on the wafer support 6, the surface of which is coated with an organic film such as a photoresist film; 8 is a wafer in the reaction tube 3; Light from the plasma in the reaction tube 3 is emitted from the excited plasma; 9 is a spectrometer entrance slit for inputting the light from the plasma in the reaction tube 3 into the spectrometer IO; 1;
Reference numeral 1 denotes a spectrometer exit slit for extracting light of a specific wavelength in the light spectrum from the plasma in the reaction tube 3 divided by the spectrometer 9, and 12 converts the light of this specific wavelength into an electrical signal. A photomultiplier tube 13 is a detection device that detects the ashing end point from the signal value from the photomultiplier tube 12.

Next, a reaction gas containing oxygen gas, such as oxygen gas or oxygen gas to which a reaction promoting gas such as CF a gas is added, is introduced into the reaction tube 3 from the zero reaction gas supply pipe 4 whose operation will be described. The reactive gas is ionized by the high frequency high electric field from the high frequency power source 1 for plasma generation, and oxygen plasma is generated. This oxygen plasma causes the organic film on the surface of the wafer 7 to undergo a reaction as shown in the following formula, and is removed from the wafer surface.

During this ashing, the light 8 emitted from the plasma gas λ in the reaction tube is used with a spectrometer 10 to obtain an emission spectrum (Hl (hydrogen atom) spectrum) regarding the reaction product shown in the above reaction formula:
56nm, CO (carbon monoxide molecule) spectrum: 2
83nm, 298nm, Ofl (hydroxyl group molecule)
Spectrum: 306nm - 316nm) Emission spectrum related to light and oxygen plasma necessary for reaction (0■
(oxygen atom) spectrum: 777 nm, Ox (oxygen molecule) spectrum: 759 nm), one light of a specific wavelength is taken out, and the detection device 13 detects the point at which the intensity change becomes stable, and the ashing is completed.

[Problem that the invention seeks to solve]

The conventional plasma ashing end point detection device is configured as described above, and does not observe changes in the intensity of light of a specific wavelength, so it only monitors the time it takes for reaction products to be discharged from the reaction tube through the reaction gas exhaust pipe. This method has disadvantages in that stabilization of emission spectrum intensity changes is delayed and detection of the end point of ashing is delayed from the actual end.

Also, it takes time for the plasma to become uniform spatially,
Since there are differences in the progress of ashing for each wafer, there is a possibility that the end point may be incorrect if only the negative points are measured. Further, the intensity and intensity changes of the emission spectrum change due to changes in ashing conditions such as changes in the number of wafers, and it is necessary to adjust the detection level of the detection device each time.

Furthermore, since the photomultiplier tube is located near the reaction tube, there is a risk that the photomultiplier tube and the detection device may malfunction due to the high frequency electric field from the high frequency power source for plasma generation.

This invention was made to solve the above-mentioned problems, and it is possible to detect the end point of ashing in synchronization with the actual end, without false detection or malfunction, and to reduce the detection level of the detection device due to changes in ashing conditions. The object of the present invention is to obtain a plasma ashing end point detection device that does not require adjustment.

[Means for solving problems]

The plasma ashing end point detection device according to the present invention detects at least two spectral line lights of b3Σ-a3π transition light in the wavelength range of 296 to 300 nm from CO (carbon monoxide molecules) in plasma in a reaction tube. The light is separated by a dispersion element and incident on a light/electrical conversion element surrounded by a conductor, which is extracted as an electrical signal to determine the rotational temperature of the plasma from the mutual light intensity, and detects changes in the rotational temperature or the vicinity of the organic coating. The end point of ashing is detected by comparing the rotational temperature of the plasma region with changes in the rotational temperature of the plasma region near the electrode.

[Effect]

In this invention, the rotational temperature of the plasma in the reaction tube during plasma ashing is as shown in FIG. 4, and the rotational temperature at the end of ashing is almost constant both on the wafer surface and in the plasma region near the electrode. However, during ashing, the rotational temperature has a characteristic of decreasing on the wafer surface and increasing near the electrode, so the rotational temperature is determined from the light intensity from the CO and the change in the rotational temperature over time is observed. Or, by comparing the rotational temperature on the wafer surface near the organic film and the rotational temperature near the electrode (in the plasma region),
The end point of ashing can be accurately and stably detected by observing the point in time when the difference between the two temperatures becomes smaller and coincides with each other, or is reversed.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, numerals 1 to 8 are exactly the same as the conventional device described above. Reference numeral 14 is a monochromator whose wavelength can be selected by an external control signal, and 15 is a wavelength dispersion element installed within the monochromator 14, which is a diffraction grating in this embodiment. 16 is a diffraction grating drive device for rotating this diffraction grating 15 and setting it at an arbitrary angle to extract a specific wavelength; 17 is a light/electric conversion element installed in a part of the output loss slit of the monochromator 14; In this embodiment, a photomultiplier tube is used. 18 is a conductor container for covering the photomultiplier tube I7 with four bodies except for the light entrance; 13 is a conductor container for controlling the diffraction grating driving device 16 and the photomultiplier tube 17;
This is a detection device that determines the rotational temperature from the output signal and detects the end point of ashing.

In the plasma ashing end point detection device configured as described above, the rotation angle of the diffraction grating is changed to extract a certain spectral line of the b'''Σ-a3π transition light from CO and input it into the photomultiplier tube. , convert the light intensity into an electrical signal, and temporarily store its maximum value 1a in the detection device.Next, rotate the diffraction grating, select another spectral line in the same way, and calculate its maximum value !b. The rotational temperature of the plasma is determined from the intensity ratio of these two, and from the change in rotational temperature, or by installing two monochromators, the rotational temperature near the organic film and the plasma near the electrode can be determined. The end point of ashing is detected by comparing the change in rotational temperature of the area.

The above operation will be explained in detail below.

Figure 2 shows wavelengths 280-294 during plasma ashing.
emission spectral distribution in the range of nm, b of CO
The spectral lines between each rotational level of the 3Σ-a3π transition light are
It is stronger than other emission spectra and well separated from other spectral lines.

The intensity I of spontaneously emitted light from the J1 state to the J2 state of molecules in the plasma is defined by the rotation temperature of the molecule as T, the transition probability from the J1 state to the J2 state as A J t J t, and the emission frequency as DJIJ! , J, the energy level of the state is EJI,
Jl state $I J Let Jl be the rotational quantum number of Z state respectively
, written by Jl and G, Hertzbarb.

“Molecular Vectra and Molecular Structure,” I Spectra of Dire, Tomic Molquières (1950) (G, Herzbe
rg+ Mo1ecular 5pectra and
1.
5pectra of Diatomic Molec
(1950), where Q, , is a state phase, and C is a proportionality constant. Taking the logarithm of both sides of the above equation, when considering the transition between rotational levels, the change in log νJIJ□ is small and can be considered as a constant, so ■ log log AJIJs(Jl
+Jz +1) C6□t: Constant ■ The rotation temperature T can be found from the slope.

As a specific example, two spectral lines λ1. λ.

Strength of 1. , Ib, the first
The svectono l/line λ, is Jl, and from the state J. For the transition light to the state, the transition probability is AatJts, the energy level of J+a state is EJla+J1m state, J, and the rotational quantum number of the state is Jllll+J! a+second spectral line λ1 from Jllt state to J. For transition light to the state, let the transition probability be AJ+bJzbz, the energy level of the Jrb state be Ex+b, and the rotational quantum numbers of the JH state and Jtb state be JIb+Job, respectively.
log A J1mJ! a log A JI
bJzb) (log AJtmJia log
Aa+bJz,,)knkm ((log I
n −1og lb )−(log (Jta
+Jzm +1) log(, Lb +, h
b+1)-(log A0mJzs+-10g A
, bJzb)) where B −1og (Jta +Jza +1)
−1o(H(Jtb +J211 +1)−(l
og AJIIIJ! 11 log AJtbJ
tb), it becomes 1og −−B ■−.

Here, A and B are constants determined in advance according to the spectral lines to be observed.

FIG. 3 is a block diagram of an example of a signal processing device for determining the rotational temperature.

The first data temporarily stored in the detection device. The intensities I,,I, of the second spectral lines are input to the divider 30, 1. /
1 is output. The signals I, /I, are converted into signals logl, /Ih by the logarithmic converter 31 in the next stage, and the preset value B is converted into logi by the subtracter 32 in the next stage.
Subtracted from m/'b, (log I a / I
b −B ) is output.

Next, the divider 33 divides the preset value A into (log
Divide by I a / I b B) to obtain.

FIG. 4 shows changes in rotational temperature during ashing and at the end of ashing on the wafer surface coated with the amorphous substance film and in the plasma region near the high-frequency electric field application electrode 2.

The ashing conditions are: 25 wafers 7, wafer support 6
The output of the high-frequency power supply 1 for plasma generation was set to 800 W at an oxygen pressure of 1.5 Torr.

As shown in FIG. 4, the rotational temperature on the wafer surface during ashing is about 120 degrees lower than at the end of ashing, and increases as ashing ends.

On the other hand, the rotational temperature of the plasma region near the electrode is about 80 degrees higher during ashing than at the end of ashing, and decreases as ashing ends.

Therefore, when the rotational temperature is determined from the spectral line intensity ratio of the CO light from the plasma during ashing and the observation position of the CO light is on the wafer surface, when the rotational temperature starts to rise or reaches a certain value. It is determined that ashing is completed.

Alternatively, if the CO light observation position is in a plasma region near the electrode, it is determined that ashing has ended when the rotational temperature begins to decrease or reaches a certain value.

Alternatively, if CO light is observed simultaneously on the wafer surface and in the plasma region near the electrode, and it is determined that ashing has ended when the difference in re-rotation temperature becomes small and matches or reverses, the detection device can be adjusted due to changes in ashing conditions, etc. is no longer necessary, and the ashing end point can be detected stably and without false detection.

In addition, since the optical/electrical conversion element is surrounded by six containers 18, the shielding performance of the optical/electrical conversion element against electromagnetic waves is improved, and the influence of the high frequency and high electric field from the high frequency power source 1 for plasma generation is greatly reduced. It can be made smaller.

In the above embodiment, an optical system for condensing light from the plasma is not installed, but a convex lens or a concave mirror may be placed in front of the monochromator 14 as a condensing optical system.

Furthermore, the conductor container 18 can be omitted by using the container for the optical/electric conversion element 17 as a hot body to achieve the same effect as the conductor container 18.

FIG. 5 shows another embodiment of the invention, in which the reflection, t
Using fl19, the light on the wafer surface and the light from the plasma region near Tt1 are incident on separate monochromators 14, and the end point of ashing is detected by observing changes in the intensity of the CO light. be.

FIG. 6 shows yet another embodiment of the invention, which uses optical fibers 20 to direct light on the wafer surface and light from the plasma region near the electrodes to separate monochromators 14.
The end point of ashing is detected by observing changes in the intensity of CO light.

FIG. 7 shows yet another embodiment of the invention, which is reflective! Ji19, a reflector B (21) whose angle changes according to an external control signal, and a reflector drive device i! that drives this reflector B. 22, the light on the wafer surface and the light from the plasma region near the electrode are alternately incident on one monochromator, and the end point of ashing is detected from the intensity change of the CO light in the two regions. In this embodiment, the control signal from the detection device 13 causes the reflector driving device i! 22 works, the reflecting mirror B (21) rotates to the position indicated by the broken line in the figure, and allows the light on the wafer surface to enter the monochromator 14 without blocking it. Thereafter, the spectral line intensity of the CO light is observed, and the rotational temperature on the wafer surface is stored in the detection device 13. Thereafter, the reflection 1B (21) returns to its original position by the control 'a signal from the detection bag W13, reflects the light from the plasma region near the electrode reflected by the reflection fi19, and makes it incident on the monochromator 14. .

After that, the spectral line intensity of the CO light is observed, the rotational temperature of the plasma region near the electrode is stored in the detection device 13, and the rotational temperature of the two regions is determined by one monochromator, and the rotational temperature of the two regions is determined by one monochromator. The end point of ashing is detected by comparison.

FIG. 8 shows yet another embodiment of the present invention, in which light from the plasma is incident on a diffraction grating as a wavelength dispersive element and the light/electronic light is transmitted to two different locations where the CO spectral line light is reflected. By arranging the conversion element 18, there is no need to provide a storage section within the detection device 13, and the rotation temperature can be determined.

Here, the same effect can be obtained even if a prism is used as the wavelength dispersion element.

FIG. 9 shows still another embodiment of the present invention, in which the rotational temperature of the plasma region on the wafer surface and in the vicinity of the electrodes is adjusted in the same way as in the embodiment of FIG. 8 by arranging two wavelength dispersion probes 15. This is what I was trying to find.

FIG. 10 shows yet another embodiment of the invention, in which light from the plasma is incident on a wavelength dispersive probe 15 and one end of an optical fiber 20 is placed at two different locations where CO spectral line light is reflected. A light/electric conversion element 17 is arranged at the other end of the optical fiber, thereby eliminating the need for a storage section in the detection device 13, facilitating light detection, and determining the rotational temperature.

FIG. 11 shows still another embodiment of the present invention, in which the rotational temperature of the plasma region on the wafer surface and near the electrodes is controlled by arranging two wavelength dispersion probes 15 in the same manner as in the embodiment of FIG. 10. This is what I was looking for.

〔Effect of the invention〕

As described above, according to the present invention, CO (carbon monoxide molecules) in the plasma in the reaction tube has a wavelength of 296 to 300.
At least two or more spectral line lights out of the b3Σ-a3π transition light in the range of nm are separated by, for example, a wavelength dispersion element and incident on an optical/electrical conversion element, thereby extracting them as electrical signals. The end point of ashing is detected by determining the rotational temperature of the plasma from the intensity and comparing the change in rotational temperature or the rotational temperature near the organic film with the change in the rotational temperature of the plasma region near the electrode. There is no need to adjust the detection device due to changes in ashing conditions, and there is an effect that a device that is stable, accurate, and does not cause false detection can be obtained at a low cost.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a plasma ashing end point detection device according to an embodiment of the present invention, FIG. 2 is a diagram showing the emission spectrum distribution in the wavelength range of 280 to 294 nm during plasma ashing, and FIG. The figure is a block diagram showing an example of a signal processing device that calculates rotational temperature from two different spectral line light intensities. Diagram M4 shows a signal processing system on the wafer surface coated with an organic film and in the plasma region near the electrode for applying a high-frequency electric field. Figure 5 shows changes in rotational temperature during ashing and at the end of ashing. Using a reflecting mirror, light on the wafer surface and light from the plasma region near the electrode are incident on separate monochromators.
FIG. 6 is a diagram showing another embodiment of the present invention in which the end point is detected by comparing the rotational temperatures of different regions, and in which light on the wafer surface and light in the plasma region near the electrode are separated using an optical fiber. Fig. 7 shows still another embodiment of the present invention, in which the rotational temperature of different regions is compared and the end point is detected by inputting the light into a monochromator, and the angle is changed by the reflecting mirror and a control signal from the outside. Another embodiment of the present invention is shown in which light on the wafer surface and light from a plasma region near the electrode are alternately incident on a monochromator using a reflecting mirror, and the end point is detected by comparing the rotational temperatures of different regions. Figure 8 shows a method of the present invention in which light from plasma is spectrally decomposed by a wavelength dispersion element, and the end point is detected by placing optical/electric conversion elements at two different positions where CO spectral line light is reflected. FIG. 9 is a diagram showing still another embodiment, in which two wavelength dispersive elements are used to spectrally decompose the light in the plasma region on the wafer surface and in the vicinity of the electrode, and the end point is detected by comparing the rotational temperatures of different regions. FIG. 10 is a diagram showing still another embodiment of the present invention, in which light from plasma is spectrally decomposed by a wavelength dispersion element, and CO spectral line light is guided to an optical/electrical conversion element through an optical fiber to detect the end point. FIG. 11 is a diagram showing still another embodiment of the present invention, in which two wavelength dispersive elements are used to
A diagram showing yet another embodiment of the present invention, in which the light in the plasma region near the electrode is separately spectrally decomposed, and the CO spectral line is passed through an optical fiber to an optical/electrical conversion element to detect the end point. , is a diagram showing a conventional plasma ashing end point detection device. In the figure, 1 is a high-frequency power source for plasma generation, 2 is an electrode for applying a high-frequency electric field, 3 is a reaction tube, 4 is a reaction gas supply tube,
5 is a reaction gas exhaust pipe, 6 is a wafer support stand, 7 is a wafer,
8 is light from the plasma in the reaction tube, 9 is a spectrometer entrance slit, 10 is a spectrometer, 11 is a spectrometer exit slit, 12
1 is a photomultiplier tube, 13 is a detection device, 14 is a monochromator, 15 is a diffraction grating, 16 is a diffraction grating drive device, 17 is an optical/electric conversion element, 18 is a four-body container, 19 is a reflecting mirror, 2
0 is an optical fiber, 21 is a reflecting mirror B122 is a reflecting mirror driving device. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (11)

[Claims] (1) In a plasma ashing end point detection device that uses oxygen plasma to remove organic films such as photoresist films, the wavelength 296 from CO (carbon monoxide molecules) in the plasma
a light detection means for detecting the light intensity of at least two spectral lines among the b^3Σ-a^3π transition light in the range of ~300 nm; and light of the two or more spectral lines detected by the light detection means. 1. A plasma ashing end point detection device, comprising: comparison means for comparing intensities to detect the end point of ashing. (2) The comparing means determines the rotational temperature of the plasma from the light intensity of the two or more spectral lines, and detects the end point of ashing from the change in the rotational temperature. The plasma ashing end point detection device described above. (3) The plasma ashing end point detection device according to claim 2, wherein the comparison means determines the rotational temperature of the plasma from light from CO in the plasma near the organic film. (4) The comparison means detects the end point of ashing using a point in time when the rotational temperature of the plasma in the vicinity of the organic film becomes larger than a certain value. Plasma ashing end point detection device. (5) The plasma ashing end point according to claim 2, wherein the comparison means determines the rotational temperature of the plasma from light from CO in a plasma region near the electrode for applying a high-frequency electric field for plasma generation. Detection device. (6) The comparison means detects the end point of ashing using the point in time when the rotational temperature of the plasma region near the electrode for applying a high-frequency electric field becomes smaller than a certain value. Plasma ashing end point detection device as described in . (7) The above-mentioned comparison means detects the end point of ashing by using the point in time when the rotational temperature of the plasma near the organic film matches or is reversed to the rotational temperature of the plasma near the electrode for applying a high-frequency electric field. The plasma ashing end point detection device according to item 2. (8) The light detection means includes a wavelength dispersion element that wavelength-disperses light from the plasma, and a light dispersion element disposed at at least two positions where the spectral line light of the transition light from CO is reflected from the wavelength dispersion element. 8. The plasma ashing end point detection device according to any one of claims 1 to 7, characterized in that the plasma ashing end point detection device comprises: /an electrical conversion element. (9) The light detection means includes a wavelength dispersion element that wavelength-disperses light from the plasma, and one end of the wavelength dispersion element at at least two or more positions where the spectral line light of the transition light from CO is reflected from the wavelength dispersion element. The plasma ashing end point detection device according to any one of claims 1 to 7, comprising an optical fiber arranged and an optical/electric conversion element arranged at the other end of the optical fiber. . (10) The light detecting means includes a monochromator arranged to receive light from the plasma and capable of selecting a wavelength that can be extracted by an external control signal; An electric conversion element and a monochromator placed after this to control the above-mentioned light/
8. A plasma ashing end point detection device according to any one of claims 1 to 7, comprising a detection device that detects an end point by obtaining an output signal from an electrical conversion element. (11) The plasma ashing end point detection device according to claim 10, wherein the optical/electrical conversion element is surrounded by a conductor.